Conventional chucks for power operated drills and the like are opened and closed by use of a key. One hand of the user must operate the key leaving the other hand available to put the drill bit in the chuck or remove it and also to hold the drill if it is portable. This requirement has brought about the development of a number of keyless or self-locking chucks, so-called, which do not require the use of both hands to close or open. One such chuck is disclosed in Whitehead U.S. Pat. No. 4,423,881 of Jan. 3, 1984. That chuck has an outer rotatable sleeve threaded to the drill-gripping elements and inertial means which cause the chuck to grip the drill stem when the user holds the sleeve in one hand and starts the drill motor. The chuck grip is released by a similar operation but in which the drill motor is reversed. All keyless chucks with which I am familiar require the user to hold such a sleeve during locking and unlocking of the chuck.
Although the sleeve need be held only for a moment while the drill motor is running, some users find this requirement objectionable. Obviously, if the sleeve is held too long the drill motor wrenches it out of the grip of the holder. Another disadvantage of existing keyless chucks is that the drill bit may drop out of the chuck if the bit is not held by hand during the opening or closing operation, or may be ejected when the chuck is opened, possibly injuring the user.